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/**
* Copyright (C) 2013 10gen Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <boost/thread/thread.hpp>
#include <boost/thread/condition.hpp>
#include "mongo/base/disallow_copying.h"
#include "mongo/platform/cstdint.h"
#include "mongo/platform/unordered_map.h"
#include "mongo/util/concurrency/mutex.h"
#include "mongo/util/time_support.h"
namespace mongo {
/**
* DeadlineMonitor
*
* Monitors tasks which are required to complete before a deadline. When
* a deadline is started on a _Task*, either the deadline must be stopped,
* or _Task::kill() will be called when the deadline arrives.
*
* Each instance of a DeadlineMonitor spawns a thread which waits for one of the
* following conditions:
* - a task is added to the monitor
* - a task is removed from the monitor
* - the nearest deadline has arrived
*
* Ownership:
* The _Task* must not be freed until the deadline has elapsed or stopDeadline()
* has been called.
*
* NOTE: Each instance of this class spawns a new thread. It is intended to be a stop-gap
* solution for simple deadline monitoring until a more robust solution can be
* implemented.
*
* NOTE: timing is based on wallclock time, which may not be precise.
*/
template <typename _Task>
class DeadlineMonitor {
MONGO_DISALLOW_COPYING(DeadlineMonitor);
public:
DeadlineMonitor() :
_tasks(),
_deadlineMutex("DeadlineMonitor"),
_newDeadlineAvailable(),
_nearestDeadlineWallclock(kMaxDeadline),
_monitorThread(&mongo::DeadlineMonitor<_Task>::deadlineMonitorThread, this) {
}
~DeadlineMonitor() {
// ensure the monitor thread has been stopped before destruction
_monitorThread.interrupt();
_monitorThread.join();
}
/**
* Start monitoring a task for deadline lapse. User must call stopDeadline() before
* deleting the task. Note that stopDeadline() cannot be called from within the
* kill() method.
* @param task the task to kill()
* @param timeoutMs number of milliseconds before the deadline expires
*/
void startDeadline(_Task* const task, uint64_t timeoutMs) {
uint64_t now = curTimeMillis64();
scoped_lock lk(_deadlineMutex);
// insert or update the deadline
std::pair<typename TaskDeadlineMap::iterator, bool> inserted =
_tasks.insert(make_pair(task, now + timeoutMs));
if (!inserted.second)
inserted.first->second = now + timeoutMs;
if (inserted.first->second < _nearestDeadlineWallclock) {
// notify the monitor thread of the new, closer deadline
_nearestDeadlineWallclock = inserted.first->second;
_newDeadlineAvailable.notify_one();
}
}
/**
* Stop monitoring a task. Can be called multiple times, before or after a
* deadline has expired (as long as the task remains allocated).
* @return true if the task was found and erased
*/
bool stopDeadline(_Task* const task) {
scoped_lock lk(_deadlineMutex);
return _tasks.erase(task);
}
private:
/**
* Main deadline monitor loop. Waits on a condition variable until a task
* is started, stopped, or the nearest deadline arrives. If a deadline arrives,
* _Task::kill() is invoked.
*/
void deadlineMonitorThread() {
scoped_lock lk(_deadlineMutex);
while (true) {
// get the next interval to wait
uint64_t now = curTimeMillis64();
// wait for a task to be added or a deadline to expire
while (_nearestDeadlineWallclock > now) {
uint64_t nearestDeadlineMs;
if (_nearestDeadlineWallclock == kMaxDeadline) {
_newDeadlineAvailable.wait(lk.boost());
}
else {
nearestDeadlineMs = _nearestDeadlineWallclock - now;
_newDeadlineAvailable.timed_wait(lk.boost(),
boost::posix_time::milliseconds(nearestDeadlineMs));
}
now = curTimeMillis64();
}
if (_tasks.empty()) {
// all deadline timers have been stopped
_nearestDeadlineWallclock = kMaxDeadline;
continue;
}
// set the next interval to wait for deadline completion
_nearestDeadlineWallclock = kMaxDeadline;
typename TaskDeadlineMap::iterator i = _tasks.begin();
while (i != _tasks.end()) {
if (i->second < now) {
// deadline expired
i->first->kill();
_tasks.erase(i++);
}
else {
if (i->second < _nearestDeadlineWallclock)
// nearest deadline seen so far
_nearestDeadlineWallclock = i->second;
++i;
}
}
}
}
static const uint64_t kMaxDeadline;
typedef unordered_map<_Task*, uint64_t> TaskDeadlineMap;
TaskDeadlineMap _tasks; // map of running tasks with deadlines
mongo::mutex _deadlineMutex; // protects all non-const members, except _monitorThread
boost::condition _newDeadlineAvailable; // condition variable for timeout, start and stop
uint64_t _nearestDeadlineWallclock; // absolute time of the nearest deadline
boost::thread _monitorThread; // the deadline monitor thread
};
template <typename _Task>
const uint64_t DeadlineMonitor<_Task>::kMaxDeadline =
std::numeric_limits<uint64_t>::max();
} // namespace mongo
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